[Ifeffit] Change in fixed baseline after fit in XAS Viewer

George Sterbinsky GeorgeSterbinsky at u.northwestern.edu
Mon May 4 12:24:06 CDT 2020


I have observed changes in fixed parameters while running a pre-edge peak
fit in XAS Viewer. I first run a baseline fit. This provides a good match
to the data in the baseline fitting region. I would like to subtract the
baseline from the data and then numerically integrate the data. In order to
export the baseline fit and data, I fix all of the fitting parameters for
bline and bpeak and then click "fit model". This generates a baseline and
fit that no longer match the data well in the baseline fitting region.
Additionally, in the "Fit Results" window, the reported best-fit values of
the fixed parameters are slightly different from the values reported in the
"Value" field after the baseline fit, to which they were fixed. This
appears to be the result of rounding of the baseline fit parameters at some
point after the baseline fit. For example bline_slope was fixed to
"-0.0024752483" but the best-fit value is "-0.00247500". I realize I am
using XAS Viewer in a way that it was not exactly designed for, and perhaps
no one anticipated someone fixing a parameter out to 10 decimal places.
However, what I am doing still seems reasonable, and I would greatly
appreciate it if XAS Viewer could be updated so that all digits entered in
the Value field for a fixed parameter will be maintained for the fit. I am
happy to provide a project file and instructions to reproduce my
observation if they would be helpful.

Thank you,
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